Beta energy extractor

ABSTRACT

The present disclosure is directed to an energy extraction device that employs a radioactive isotope, such as  90 Sr, as a charged particle source. The decaying radioactive isotope emits energetic charged particles, such as beta particles, into a magnetic field. Because the magnetic field is substantially normal to the paths of the charged particles, a force is induced on the charged particles normal to both the path and the magnetic field. The induced force causes the charged particles to assume circular paths, forming a circulating charged particle beam that is contained within a structure. The circulating charged particle beam emits cyclotron radiation. The structure includes one or more rectennas around the interior wall which convert the cyclotron radiation to electrical energy as a direct current voltage.

BACKGROUND

1. Field

The present disclosure relates crossed-field devices using radioactiveisotopes. Particularly, this disclosure relates to power generation incrossed-field devices employing radioactive isotopes.

2. Description of the Related Art

Power systems providing electrical power for spacecraft havetraditionally utilized solar energy or radioactive materials as a powersource. Solar power systems, employing solar cells to capture power fromthe sun and convert it to electrical energy, are often used in satelliteapplications where the spacecraft remains within reasonable proximityand view of the sun. Among power systems using radioactive isotopes(radioisotopes) as fuel in space applications, there are two significanttypes, reactor-based systems and radioisotope thermal generators (RTGs).Although a typical RTG delivers less power than a typical reactor-basedsystem, reactor-based power systems are much more complex and lessreliable than RTGs.

A radioisotope thermal generator (RTG) is a solid state electricaldevice which develops electrical power from a decaying radioisotope. Atypical RTG comprises a central core of a decaying radioisotope, such as²³⁸Pu. The radioisotope generates heat as it decays. The RTG convertsthe heat energy of a decaying radioisotope into electricity through anarray of thermocouples. A thermocouple converts thermal energy directlyinto electrical energy. For example, a thermocouple may be made of twometal materials that can both conduct electricity. They are connected toeach other in a closed electrical circuit. If the two metals are atdifferent temperatures, an electric current will flow in the circuitdelivering electrical power. Excess heat energy is rejected from theRTG. Due to the use of the radioisotope, the entire RTG must be properlyshielded.

Unfortunately, conversion of the heat energy to electricity makes RTGsvery inefficient. RTGs operate with an energy conversion efficiency ofless than ten percent, typically less than five percent. Most of theenergy from the decaying radioisotope is lost as excess thermal energyand must be rejected from the spacecraft. Thus, RTGs waste much of theavailable energy from the decaying radioisotope. In addition, RTGs arerelatively expensive to manufacture (although not as expensive asreactor-based power systems).

In view of the foregoing, there is a need in the art for power systemsin space applications that are simple, reliable, safe and lessexpensive. Further, for power systems which employ radioactive isotopes,there is a need for such power systems to obtain higher energyconversion efficiencies. As detailed hereafter, these and other needsare satisfied by the present disclosure.

SUMMARY

The present disclosure is directed to an energy extraction device thatemploys a radioactive isotope, such as ⁹⁰Sr, as a charged particlesource. The decaying radioactive isotope emits energetic chargedparticles, such as beta particles, into a magnetic field. Because themagnetic field is substantially normal to the paths of the chargedparticles, a force is induced on the charged particles normal to boththe path and the magnetic field. The induced force causes the chargedparticles to assume circular paths, forming a circulating chargedparticle beam that is contained within a structure. The circulatingcharged particle beam emits cyclotron radiation. The structure includesone or more rectennas around the interior wall which convert thecyclotron radiation to electrical energy as a DC voltage.

In general, an apparatus embodiment comprises a radioactive means foremitting charged particles, means for receiving the circulating chargedparticle beam, means for inducing a magnetic field substantially normalto movement of the emitted charged particles and producing a circulatingcharged particle beam yielding electromagnetic radiation, and rectennameans for converting the electromagnetic radiation to a voltage.

In one example, a typical apparatus embodiment of the disclosurecomprises a radioactive isotope emitting charged particles, a chamberreceiving the emitted charged particles, one or more magnets disposed toprovide a magnetic field across the chamber and substantially normal tomovement of the emitted charged particles to produce a circulatingcharged particle beam within the chamber, the circulating chargedparticle beam yielding electromagnetic radiation, and one or morerectennas disposed proximate to the circulating charge particle beam,each converting the electromagnetic radiation to a voltage at an output.The radioactive isotope may be disposed centrally within the chamber.The one or more magnets may comprise a plurality of permanent magnetsdisposed at opposing sides of the chamber.

The chamber may be cylindrical with the magnetic field provided along alength of the cylindrical chamber. In this case, the one or more magnetsmay comprise a plurality of permanent magnets disposed at opposing endsof the cylindrical chamber. In addition, the one or more rectennas maycomprise a plurality of rectennas disposed around an interior wall ofthe cylindrical chamber.

In some embodiments of the disclosure, the charged particles maycomprise beta particles and the radioactive isotope is selected from thegroup consisting of 90Sr, 106Ru, 144Pm, 170Tm, 137Cs, and 144Ce.Alternately, the charged particles may comprise alpha particles and theradioactive isotope is selected from the group consisting of 238Pu,210Po, 242Cm, and 244Cm.

In a similar manner, a typical method embodiment comprises the steps ofemitting charged particles from a radioactive isotope, receiving theemitted charged particles within a chamber, providing a magnetic fieldacross the chamber and substantially normal to movement of the emittedcharged particles with one or more magnets to produce a circulatingcharged particle beam within the chamber, generating electromagneticradiation from the circulating charged particle beam, and converting theelectromagnetic radiation to a voltage at an output with each of one ormore rectennas disposed proximate to the circulating charge particlebeam. Method embodiments of the disclosure may be further modifiedconsistent with apparatuses and systems described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1A a top view of a moving electron directed into a circular pathunder a magnetic field;

FIG. 1B illustrates developing a circulating charged particle beam froma radioactive isotope;

FIG. 2A illustrates a top view of an example rectenna that may be usedin an embodiment of the disclosure;

FIG. 2B illustrates a side view of the example rectenna including abasic circuit that may be used in an embodiment of the disclosure;

FIG. 2C illustrates a plurality of rectennas in an array coupledtogether that may be employed in an example embodiment;

FIG. 3A is a schematic diagram of an energy extraction device that usesa radioactive isotope charged particle source and rectennas;

FIG. 3B illustrates a top view of an energy extraction device that usesa radioactive isotope charged particle source and rectennas; and

FIG. 4 is a flowchart of an exemplary method of operating an energyextraction device employing a radioactive isotope charged particlesource and rectennas.

DETAILED DESCRIPTION

In the following description of the preferred embodiment, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration a specific embodiment in which thedisclosure may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present disclosure.

1. Circulating Charge Particle Beam from a Radioactive Isotope

Crossed-field devices are a class of electronic devices which employ amagnetic field (B-field) and an electric field (E-field) at right anglesto one another operating upon a flow of electrons. One application forsuch devices has been to elicit high frequency electromagnetic radiationfrom a transfer of energy from electrons moving in a plane normal to anapplied magnetic field. Typically an electric field is used to drive themotion of the electrons. Thus, the driving electric field is normal(i.e., crossed) to the magnetic field. For a discussion of variouscrossed-field devices, see “High Power Microwave Sources” VictorGranatstein and Igor Alexeff, Editors, Artech House, Inc., 1987, pp.309-327, which is incorporated by reference herein. However, embodimentsof the present disclosure harness electrons (or other charged particles)emitted from a radioactive isotope at a relatively high velocity asdescribed hereafter rather than accelerate electrons under an electricfield. The physics behind developing a circulating electron beam from aradioactive isotope are described here.

When an electron is accelerated by a potential V, its relativistickinetic energy is given by the following equation.m ₀(γ−1)c ² =eV  (1)This may be approximated as follows in non-relativistic limit where m₀is the rest mass of the electron.

$\begin{matrix}{{{{m_{0}( {\gamma - 1} )}c^{2}} \approx {{m_{0}( {1 + {\frac{1}{2}\frac{v^{2}}{c^{2}}} - 1} )}c^{2}}} = {{\frac{1}{2}m_{0}v^{2}} = {eV}}} & (2)\end{matrix}$Solving equation (3) in terms of v, yields the following.

$\begin{matrix}{{{m_{0}( {\gamma - 1} )}c^{2}} = {{{m_{0}( {\frac{1}{\sqrt{1 - \frac{v^{2}}{c^{2}}}} - 1} )}c^{2}} = {eV}}} & (3)\end{matrix}$Equation (3) can be further reduced to the following result.

$\begin{matrix}{{v = {( \frac{\sqrt{1 + \frac{2m_{0}c^{2}}{eV}}}{1 + \frac{m_{0}c^{2}}{eV}} )c}}\;} & (4)\end{matrix}$From equation (4), an electron accelerated by 3MV, a typical Betaemitter decay energy, potential has a speed determined below.

$\begin{matrix}{v = {{( \frac{\sqrt{1 + \frac{2 \times 9.1 \times 10^{- 31} \times ( {3 \times 10^{8}} )^{2}}{1.6 \times 10^{- 19} \times 3 \times 10^{6}}}}{1 + \frac{9.1 \times 10^{- 31} \times ( {3 \times 10^{8}} )^{2}}{1.6 \times 10^{- 19} \times 3 \times 10^{6}}} )c} = {{( \frac{\sqrt{1 + 0.3415}}{1 + 0.1706} )c} = {0.99c}}}} & (5)\end{matrix}$

FIG. 1A is a top view of a moving electron directed into a circular pathunder a magnetic field 100. The electron 102 with velocity v is passingthrough a uniform magnetic field 100 perpendicular to the page and isaccordingly subject to the Lorentz force 104 given by the followingequation.F=evB  (6)The centripetal force on the electron is given as follows.

$\begin{matrix}{F = {\frac{m\; v^{2}}{r} = \frac{m_{0}\gamma\; v^{2}}{r}}} & (7)\end{matrix}$We can solve equations (6) and (7) together, and apply equation (3) toyield an expression of γ.

$\begin{matrix}{B = {{\frac{m_{0}}{er}( {\frac{eV}{m_{0}c^{2}} + 1} )( \frac{\sqrt{1 + \frac{2m_{0}c^{2}}{eV}}}{1 + \frac{m_{0}c^{2}}{eV}} )c} = {{\frac{m_{0}}{er}\frac{eV}{m_{0}c^{2}}\sqrt{1 + \frac{2m_{0}c^{2}}{e\; V}}c} = {\frac{1}{r}\frac{V}{c}\sqrt{1 + \frac{2m_{0}c^{2}}{e\; V}}}}}} & (8)\end{matrix}$

This becomes the following in a non-relativistic limit.

$\begin{matrix}{B^{2} = {{{\frac{1}{r^{2}}\frac{V^{2}}{c^{2}}( {1 + \frac{2m_{0}c^{2}}{e\; V}} )} \approx {\frac{1}{r^{2}}\frac{V^{2}}{c^{2}}( \frac{2m_{0}c^{2}}{e\; V} )}} = {{\frac{2m_{0}V}{{er}^{2}}\mspace{14mu}{or}\mspace{14mu} V} = \frac{{eB}^{2}r^{2}}{2m_{0}}}}} & (9)\end{matrix}$Equation (9) represents the Hull cut-off condition, which provides therelationship between magnetic field B and anode voltage V (assuming azero cathode voltage) when an electron is bent enough so that noelectron will hit the anode so that there is no anode current, e.g. asin a typical non-relativistic magnetron. Therefore, the magnetic fieldrequired to confine an electron with 3 MeV kinetic energy on thecircular orbit with radius 10 cm is given by the following relation(where units are all MKS).

$\begin{matrix}{B = {{\frac{1}{r}\frac{V}{c}\sqrt{1 + \frac{2m_{0}c^{2}}{eV}}} = {{\frac{3 \times 10^{6}}{0.1 \times 3 \times 10^{8}}\sqrt{1 + 0.3415}} = {{0.116\mspace{20mu} T} = {1.16\mspace{20mu} K\;{Gauss}}}}}} & (10)\end{matrix}$It can be shown that developing a magnetic field of this strength ispossible and practical.

For example, Dexter Magnetic Technology's website(http://www.dextermag.com) provides a magnetic field strength calculatorfor various permanent magnet topologies. Among them, a permanent magnetdipole calculator is provided which presents topology similar to whatmay be employed in a typical embodiment of the disclosure. A steel yokein a “C” configuration supports two rectangular permanent magnets heldat the ends to form a gap for the magnetic field. The width (W) andlength (L) are the facing areas of the magnets and the height (H) is thegap measurement between them. An example permanent magnet structure mayhave the overall dimension of 5″(W)×5″(L)×5″(H) with a 0.5″ thick magneton each side. A residual Induction (B_(r)) of 13 KGauss is a reasonablenumber for the selected example material of Nd—Fe—B. This yields anestimated magnetic field strength of approximately 1.4 K Gauss at thecenter where the magnetic field is the weakest. In another example, theoverall dimensions of the structure are 5″(W)×5″(L)×3″(H) for anotherpair of 0.5″ thick Nd—Fe—B permanent magnets. In this case, the magneticfield is approximately 2.4 K Gauss at the center where the magneticfield is the weakest. The stronger B field is a result of having shortergap dimension (closer to the dipole).

FIG. 1B illustrates developing a circulating charge particle beam from aradioactive isotope. The device 120 includes a centrally disposedradioactive isotope 122 within a chamber that emits charged particles128 such as beta particles (i.e., electrons). For example, theradioactive isotope emitting beta particles may be selected from thegroup consisting of ⁹⁰Sr, ¹⁰⁶Ru, ¹⁴⁴Pm, ¹⁷⁰Tm, ¹³⁷Cs, and ¹⁴⁴Ce. Theemitted charged particles 128 are moving at a high velocity and underthe influence of a magnetic field 126 induced by a pair of permanentmagnets 124A, 124B disposed on opposite sides of the chamber. Thepermanent magnets 124A, 124B may be coupled by a steel yoke (not shown)as is known in the art to improve the magnetic field 126 strength. Thehigh velocity charged particles 128 under the influence of the magneticfield 126 are directed into a circular path 130. It should be noted thatalthough statistically, there may be some overlap in the circular pathof ejected particles and the opposite side of the radioactive isotopesource, because the particles have the same electric charge as theradioactive isotope source, they will repel each other, resulting in thecirculating electron beam. This is a consequence of the space chargeeffect. Thus, it is demonstrated above that achieving a sufficientmagnetic field strength from commercially available permanent magnetmaterials to confine the relativistic electron is feasible withreasonable dimensions for a portable power source application asdescribed hereafter.

It should also be noted that other radioactive isotopes emitting othercharged particles may also be developed into functioning devicesaccording to the principle of the disclosure described herein. Forexample, a radioactive isotope selected from the group consisting of²³⁸Pu, ²¹⁰Po, ²⁴²Cm, and ²⁴⁴Cm emits alpha particles which can also beharnessed in a device, such as those described above. However, it isimportant to note that characteristics of different charged particles,e.g. energy, charge, etc., will require adjustments in the designparameters. For example, because alpha particles usually possess morekinetic energy (5 MeV or more) than beta particles, stronger magneticfields will be required to yield the circulating charged particle beam.In addition, the positive charge of the alpha particles will require aninversed magnetic field to induce circulation in the same direction asthe beta particles. Such adjustments to accommodate different chargedparticles from different radioactive isotopes shall be apparent to thoseskilled in the art. However, it should be noted that an embodimentemploying an alpha particle source will be significantly more difficultto implement and may be impractical in many cases. For example, it ismuch more difficult to confine alpha particles due to their mass, whichis much greater than alpha particles (i.e., electrons). This is evidentfrom Equation (10) as will be understood by those skilled in the art.

The cyclotron radiation frequency due to electron circulating inside achamber due to the magnetic field B is given by the plasma frequency perthe following equation. Cyclotron radiation is yielded as a narrow lineof emission at the frequency of the cyclotron orbit per Equation (11)below. In addition, the cyclotron radiation comprises smaller spikes at2ω and 3ω. Cyclotron radiation is described in section 5.1 ofhttp://casa.colorado.edu/˜wcash/APS3730/textbook.htm, which isincorporated by reference herein.

$\begin{matrix}{\omega = {\frac{eB}{2\pi\; m_{e}c} = {\frac{4.8 \times 10^{- 10}B}{2\;\pi \times 0.91 \times 10^{- 27} \times 3 \times 10^{10}} = {2.8 \times 10^{6\mspace{20mu}}{B({Hz})}}}}} & (11)\end{matrix}$Applying the estimated magnetic field of 2.4 K Gauss calculated from theexample magnet above, the frequency of the radiation is given asfollows. Cyclotron radiation decays exponentially. For example, it takesabout a minute to lose approximately 63%, i.e., (1-1/e), of energy ofcyclotron radiation where B=2.4 KGauss. Cyclotron losses are describedIbid., section 5.2, which is incorporated by reference herein.ω=2.8×10⁶×2.4×10³ (Hz)=6.7 GHz  (12)As previously mentioned, embodiments of the disclosure convert thecyclotron radiation to a voltage using one or more rectennas. Someexample rectenna structures are described in the next section.2. Rectenna Electromagnetic Energy Conversion

Embodiments of the disclosure operate using one or more rectennas toreceive and convert electromagnetic radiation to a voltage. Such devicescan yield efficiencies typically above fifty percent. A rectennacombines a receiving antenna (e.g., a patch antenna) for electromagneticradiation at a frequency and a rectifying circuit for converting thefrequency of the received electromagnetic radiation signal to a directcurrent voltage as is known in the art. Embodiments of the disclosuremay be implemented with any suitable known rectenna structure designedto operate in the applicable frequency range of the cyclonic radiationfrom the circulating charged particle beam, e.g., approximately 6.7 GHz.

FIG. 2A illustrates a top view of an example rectenna 200 that may beused in an embodiment of the disclosure. The rectenna 200 may beconstructed as planar microstrip patch antenna comprising a frontconductive patch 202 for receiving incident radiation disposed on asubstrate material 204. The substrate material 204 may be a dielectricmaterial such as many circuit board materials, e.g., Flame Resistant(FR4), RT 6010 and RT 5870 and other duroids or polyimides. The patch iscoupled to a probe 206 from the backside of the substrate 204 (althoughother probe configurations are possible as well).

FIG. 2B illustrates a side view of the example rectenna 200 including abasic rectifying circuit 220 that may be used in an embodiment of thedisclosure. A ground plane 208 of conductive material is disposed on thebackside of the substrate material 204. Both the ground plane 208 andthe conductive patch 202 may be formed from conductive metals asemployed in printed circuit board construction. The ground plane 208 iscoupled to the patch 202 through a coil 210 to the probe 206. The patch202 is also coupled to the Schottky diode 212 through the probe 206 toallow a current flow from the patch 202. The opposite side of the diode212 is coupled to the ground plane 208 through an RF load 214. Theoutput DC voltage 216 is delivered across the RF load 214. As used inthe beta energy extraction device, the output voltage 216 may be appliedto power electronics directly (after power conditioning) or to storeelectrical energy in a battery power storage system to be used later.

FIG. 2C illustrates a plurality of rectennas in an array 220 coupledtogether that may be employed in an example embodiment. The array 220comprises a plurality of individual rectennas 222 (nine in the example)that are electrically coupled (ganged) at their DC voltage outputs 224and applied to a load 226. The electrical configuration of one examplerectenna 228 of the array 220 is shown. The rectenna 228 comprises afront conductive patch 230 that is coupled to a waveguide 232. Thewaveguide 232 leads RF output from the conductive patch 230 a diode 234(e.g., a Schottky diode). A coil 236 is coupled to a ground plane 238,separated a distance from the conductive patch 230 by the substrate 240of the array 220, and provides a DC short circuit (ground) based on atypical LRC (inductor, capacitor & resister) circuit. A radial stub 242may coupled to the diode 234 to filter out any unwanted harmonicsgenerated by antenna element, i.e. as a bandstop filter. It should benoted that although the rectenna array is shown in FIG. 2C as a planararray, the rectenna array may also be formed onto a curved surface intoa cylindrical chamber wall as illustrated in the examples of the nextsection. Some loss of efficiency may result. Alternately, a rectennaarray around a cylindrical wall may be formed from multiple flatindividual rectannas that is actually a polygon (viewed from above).

As described, embodiments of the disclosure employ one or more rectennasdesigned to convert the selected cyclotron radiation frequency, e.g.,6.7 GHz. Any properly sized suitable known rectenna design may be usedas will be understood by those skilled in the art. For example, e.g.,Heikkenen et al., “Planar Rectennas for 2.45 GHz Wireless PowerTransfer”, IEEE 0-7803-6267-5, 2000 and Akkermans et al., “AnalyticalModels for Low-Power Rectenna Design, IEEE 1536-1225, 2005, which areboth incorporated by reference herein. The rectenna in a frequency rangearound the example frequency of approximately 6.7 GHz is wellunderstood. The magnitude of power yielded is a function of the quantityof radioactive isotope. Those skilled in the art will appreciate thatrectenna efficiency can be traded with the amount of isotope useddepending upon the application, e.g. a battery application.

3. Energy Extraction Devices Using a Radioisotope Charged ParticleSource

FIG. 3A is a schematic diagram side view of an energy extraction device300 that uses a radioactive isotope 302 charged particle source and oneor more rectennas 304. The radioactive isotope 302 is disposed centrallywithin the cylindrical chamber 316. A support for radioactive isotope302 may be constructed by any configuration and materials known in theart. For example, a platform can be wrapped around metallic rod(comprising the radioactive isotope 302) in the center of thecylindrical chamber 316 and supported by two end caps dipole magnets ofthe end caps, e.g., magnets 308A, 308B. A magnetic field 306 is appliedaxially across the cylindrical chamber 316 by permanent magnets 308A,308B disposed at opposing ends. The magnetic field 306 causes theemitted and energized charged particles 310 to spiral outward incircular paths rather than moving directly to the wall 312 of thecylindrical chamber 316. The charged particles 310 form a circulatingelectron beam 314 within the cylindrical chamber 316 as previouslydescribed.

The circulating electron beam 314 generates cyclotron electromagneticradiation 318 of a particular frequency according to the analysis in theprior section. The electromagnetic radiation 318 is then received by therectennas 304 disposed on the wall 312 of the cylindrical chamber 316.The rectennas 304 convert the received electromagnetic radiation 318 toa voltage as previously described and detailed in FIGS. 2A & 2B. Theindividual output voltages of the rectennas 304 may be combined inseries or parallel to yield an output voltage 320 of the device 300.They output voltage 320 may be applied to battery storage or directly topower electrical systems or both. For example, a particular energyextractor may yield enough DC energy such that a portion of the energyis used to power the various systems (e.g. transponders, control systemson a spacecraft) while the remaining energy is used to charge a batteryfor later use.

Because the magnetic field 306 provides the only influence on thecharged particles 310 emitted by the radioactive isotope 302, propertuning of the device 300 may be accomplished by varying the magneticfield 306 in operation. Accordingly, permanent magnets 308A, 308B maycomprise an electromagnet which can be used to tune the magnetic field306. The electromagnet may replace or combine with the permanent magnets308A, 308B to operate the device 300.

FIG. 3B illustrates a top view of an energy extraction device 300 shownin FIG. 3A that uses a radioactive isotope 302 charged particle 310source and rectennas 304. The one or more rectennas 304 may be disposedaround the wall 312 of the cylindrical chamber 316. Thus, most of theinterior surface of the wall 312 of the cylindrical chamber 316 may beused for rectennas 304.

A force will be exerted on an each charged particle 310 emitted by theradioactive isotope 302 and moving through a magnetic field 306 that isnormal to both the magnetic field 306 (refer to FIG. 3A) and to the pathof the charged particle 310. The direction of the force causes thecharged particle 310 to follow a curved path rather than a straightline. (Refer to FIGS. 1A & 1B.) This may be applied to the device 300 ofFIGS. 3A & 3B. The upper magnet 308A is a south pole and the lowermagnet 308B is a north pole. The magnetic field 306 causes their pathsto bend resulting in circular trajectories within the chamber 316. Thecharged particles 310 are emitted from the radioactive isotope 302already with relatively high energy. For example, ⁹⁰Sr emits betaparticles having a kinetic energy of approximately 2-3 MeV. As long asthe charge particles are circling inside the chamber (e.g. a vacuumcylinder), they will lose their kinetic energy completely through thecyclotron radiation. The amount of energy converted depends on theefficiency of the particular rectenna. However, a typical rectennaefficiency should yield approximately 60% to 70% of the isotope energyconverted to DC power. Once the charged particles lose all their kineticenergy, they will be absorbed to nearby material, e.g., the chamber wallor magnet, which will accumulate negative charges. These accumulatedcharges can be discharged.

It should also be noted that the overall device 300 structure includingthe chamber 316 may further include additional shielding and othersuitable structural elements that are typically employed in devices thatutilize radioactive isotopes as known in the art.

To implement embodiments of the disclosure using beta particles (havinga charge substantially identical to an electron) various radioactiveisotopes are possible. For example, the radioactive isotope emittingbeta particles may be selected from the group consisting of ⁹⁰Sr, ¹⁰⁶Ru,¹⁴⁴Pm, ¹⁷⁰Tm, ¹³⁷Cs, and ¹⁴⁴Ce. It should also be noted that otherradioactive isotopes emitting other charged particles may also bedeveloped into functioning devices according to the principle of thedisclosure. For example, a radioactive isotope selected from the groupconsisting of ²³⁸Pu, ²¹⁰Po, ²⁴²Cm, and ²⁴⁴Cm emits alpha particles whichcan be harnessed in a crossed magnetic field device, such as thosedescribed above. However, it is important to note that characteristicsof different charged particles, e.g. energy, charge, etc., will requireadjustments in the design parameters. For example, because alphaparticles usually possess more kinetic energy (5 MeV or more) than betaparticles, stronger magnetic fields will be required.

FIG. 4 is a flowchart of an exemplary method 400 of extracting energyfrom a radioactive isotope charged particle source. The method 400begins with a step 402 of emitting charged particles from a radioactiveisotope. Next, the emitted charged particles are received within achamber in step 404. Following this, a magnetic field is provided acrossthe chamber with one or more magnets substantially normal to movement ofthe emitted charged particles to produce a circulating charged particlebeam within the chamber in step 406. Next in step 408 electromagneticradiation is generated from the circulating charged particle beam.Finally in step 410, the electromagnetic radiation is converted to avoltage at an output with each of one or more rectennas disposedproximate to the circulating charge particle beam. The method 400 may befurther modified consistent with the exemplary devices described above.

This concludes the description including the preferred embodiments ofthe present disclosure. The foregoing description including thepreferred embodiment of the disclosure has been presented for thepurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure to the precise forms disclosed.Many modifications and variations are possible within the scope of theforegoing teachings. Additional variations of the present disclosure maybe devised without departing from the inventive concept as set forth inthe following claims.

What is claimed is:
 1. An apparatus, comprising: a radioactive isotopeemitting charged particles; a chamber receiving the emitted chargedparticles; one or more magnets disposed to provide a magnetic fieldacross the chamber and substantially normal to movement of the emittedcharged particles to produce a circulating charged particle beam withinthe chamber, the circulating charged particle beam yieldingelectromagnetic radiation; and one or more rectennas disposed proximateto the circulating charge particle beam, each converting theelectromagnetic radiation to a voltage at an output.
 2. The apparatus ofclaim 1, wherein the one or more magnets comprises a plurality ofpermanent magnets disposed at opposing sides of the chamber.
 3. Theapparatus of claim 1, wherein the radioactive isotope is disposedcentrally within the chamber.
 4. The apparatus of claim 1, wherein thechamber is cylindrical and the magnetic field is provided along a lengthof the cylindrical chamber.
 5. The apparatus of claim 4, wherein the oneor more magnets comprises a plurality of permanent magnets disposed atopposing ends of the cylindrical chamber.
 6. The apparatus of claim 4,wherein the one or more rectennas comprise a plurality of rectennasdisposed around an interior wall of the cylindrical chamber.
 7. Theapparatus of claim 6, wherein the one or more magnets comprises aplurality of permanent magnets disposed at opposing ends of thecylindrical chamber and the radioactive isotope is disposed centrallywithin the chamber.
 8. The apparatus of claim 1, wherein the chargedparticles comprise beta particles and the radioactive isotope isselected from the group consisting of ⁹⁰Sr, ¹⁰⁶Ru, ¹⁴⁴Pm, ¹⁷⁰Tm, ¹³⁷Cs,and ¹⁴⁴Ce.
 9. The apparatus of claim 1, wherein the charged particlescomprise alpha particles and the radioactive isotope is selected fromthe group consisting of ²³⁸Pu, ²¹⁰Po, ²⁴²Cm, and ²⁴⁴Cm.
 10. A method,comprising the steps of: emitting charged particles from a radioactiveisotope; receiving the emitted charged particles within a chamber;providing a magnetic field across the chamber and substantially normalto movement of the emitted charged particles with one or more magnets toproduce a circulating charged particle beam within the chamber;generating electromagnetic radiation from the circulating chargedparticle beam; and converting the electromagnetic radiation to a voltageat an output with each of one or more rectennas disposed proximate tothe circulating charge particle beam.
 11. The method of claim 10,wherein the one or more magnets comprises a plurality of permanentmagnets disposed at opposing sides of the chamber.
 12. The method ofclaim 10, wherein the radioactive isotope is disposed centrally withinthe chamber.
 13. The method of claim 10, wherein the chamber iscylindrical and the magnetic field is provided along a length of thecylindrical chamber.
 14. The method of claim 13, wherein the one or moremagnets comprises a plurality of permanent magnets disposed at opposingends of the cylindrical chamber.
 15. The method of claim 13, wherein theone or more rectennas comprise a plurality of rectennas disposed aroundan interior wall of the cylindrical chamber.
 16. The method of claim 15,wherein the one or more magnets comprises a plurality of permanentmagnets disposed at opposing ends of the cylindrical chamber and theradioactive isotope is disposed centrally within the chamber.
 17. Themethod of claim 10, wherein the charged particles comprise betaparticles and the radioactive isotope is selected from the groupconsisting of ⁹⁰Sr, ¹⁰⁶Ru, ¹⁴⁴Pm, ¹⁷⁰Tm, ¹³⁷CS, and ¹⁴⁴Ce.
 18. Themethod of claim 10, wherein the charged particles comprise alphaparticles and the radioactive isotope is selected from the groupconsisting of ²³⁸Pu, ²¹⁰Po, ²⁴²Cm, and ²⁴⁴CM.
 19. An apparatus,comprising: a radioactive means for emitting charged particles; meansfor receiving the circulating charged particle beam; means for inducinga magnetic field substantially normal to movement of the emitted chargedparticles and producing a circulating charged particle beam yieldingelectromagnetic radiation; and rectenna means for converting theelectromagnetic radiation to a voltage.
 20. The apparatus of claim 19,wherein the charged particles comprise beta particles.